Diagnosing diseases can involve using platforms that analyze a wide range of biomarkers. Examples of current techniques for detecting biomarkers include culture enrichment techniques for detecting target cells; ELISA for detecting proteins; and DNA microarrays for detecting nucleic acids. These techniques suffer from a few limitations: 1) they can be time consuming, often requiring several days to complete; 2) they can be expensive, running from tens to thousands of dollars per test; and 3) they can be complex, requiring skilled technicians working in specialized laboratories. These limitations have impeded the development of low-cost clinical diagnostics that can be used affordably in pharmacies, doctors' offices, and even by patients in the home.
Lateral flow immunochromatographic assays, also known as “dipsticks” or “rapid tests”, have enabled point-of-care commercial tests for some proteins present in high concentration (i.e., nanomolar), such as pregnancy tests or HIV tests. These tests can be detected by eye, or by simple optical detectors. Glucose tests, based on catalytic electrochemical sensors, can detect some high abundance small molecules, with glucose testing being the major commercial application. Some microfluidic devices offer the possibility to detect cells, viruses, bacteria, nucleic acids, and low concentration proteins (i.e., sub-picomolar).